FIG. 1A is a perspective view of an exemplary medical injection system 100 (the ACIST CVi® system) for delivering a contrast agent into a patient's vascular system for medical imaging. FIG. 1A illustrates a first fluid reservoir 132 for supplying a syringe-type positive displacement pump of a pressurizing unit 130, via a fill tubing line 27-F, and an injection tubing line 27-I coupled to unit 130 for injection of, for example, a radiopaque contrast agent, into a patient's vascular system via an inserted catheter (not shown), for example, coupled to a patient tubing line 122 at a connector 120 thereof. FIG. 1A further illustrates a second fluid reservoir 138 from which a diluent, such as saline, is drawn by a peristaltic pump 106 through yet another tubing line 128 that feeds into tubing line 122. A manifold valve 124 and associated sensor 114 control the flow of fluids into tubing line 122, from pressurizing unit 130 and from tubing line 128.
Although not shown in FIG. 1, the syringe-type positive displacement pump of unit 130 includes a fill port and an injection port to which tubing lines 27-F and 27-I, respectively are coupled; a check valve (not shown) in line 27-F and valve 124 in line 27-I are employed to control flow through tubing lines 27-F and 27-I. For example, when the pump of unit 130 is activated to draw in fluid from reservoir 132, flow from tubing lines 122 and 128 through injection tubing line 27-I is blocked by valve 124; and, after the pump is filled, when the pump is activated to pressurize the fluid therein, valve 124 is opened to allow flow of the pressurized fluid through line 27-I and into line 122, while flow through fill tubing line 27-F is blocked by the aforementioned check valve. A variety of alternative valve mechanisms for controlling the flow through tubing lines of medical injection systems, such as tubing lines 27-F and 27-I of injection system 100, are known in the art. For example, a suitable pinch valve apparatus is described in commonly-assigned U.S. Pat. No. 8,152,780. Yet, there is still a need for improved valve apparatus that simplify and increase the efficiency of valve operation to control flow in medical injection systems.